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Discussion Starter #1
Having a strange issue I'm hoping to get some suggestions for. This is a 1998 Passat.

Symptoms: at high RPMs, the red battery light will flicker. This ought be at highway speeds or it can happen when I simply rev the engine while standing still.

What I've tried so far:
- replace alternator
- replace serpentine belt tensioner
- checked connections at alternator and battery

From reading other posts on this forum and others, this is the typical problem areas. If anyone has other suggestions of what else this could be, I would be grateful.

Frank
 

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Sounds like a flaky sense wire to me. (That's the little wire that plugs into the alt.)
 

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Discussion Starter #3
Bump. Still seeing this issue. As another troubleshooting measure, hooked up a digital volt meter to the cigar lighter so I could observe the voltage while driving. The voltage is steady at about 13.8V. And the battery doesn't die, so I know I'm not going to get stranded. But dang it if it doesn't bother the crud out of me.

Thanks.
 

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I'm with sirwired, that there is a flaky connection, somewhere in the sense wire circuit to the cluster. You might try removing the cluster and WD-40 spraying all the wiring connections, which is what I do whenever a connector is accessible.
 

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So, have you traced (or done something to) the sense wire, or did you not see my last post?
 

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It could be a bad connection in the sense wire, but as it only happens at high RPM it's more likely worn brushes.
Either way if you don't fix it soon, you are likely to get stranded.
 

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Discussion Starter #7
Hi, thanks for the continued help. Regarding the last two posts, the alternator is brand new, so brushes shouldn't be it, and there was no change in behavior from before I changed the alternator. Regarding the sense wire, I did touch it of course when I installed the new alternator, but I did not trace it back to wherever it goes under the dash. Any suggestions on that would be appreciated.
 

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Assuming you have an AEB, Haynes shows the blue wire from the alternator, going to term 50 on the ign switch and to the cluster.


From the alternator the blue wire goes through 1 (from Aug98) or 2 (to Jul98) connectors to the lamp in the cluster and to one of the following (depending on MY)
Up to July 1998 - Ignition/starter switch term D/50
From August 1998 - T10k - 10-pin connector, grey, left A-pillar coupling station


You probably have a fault in the cluster, but it could be in the wiring (including power supply to cluster), or much less likely the ignition switch.
 

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Having a strange issue I'm hoping to get some suggestions for. This is a 1998 Passat.

Symptoms: at high RPMs, the red battery light will flicker. This ought be at highway speeds or it can happen when I simply rev the engine while standing still.

What I've tried so far:
- replace alternator
- replace serpentine belt tensioner
- checked connections at alternator and battery

From reading other posts on this forum and others, this is the typical problem areas. If anyone has other suggestions of what else this could be, I would be grateful.

Frank
My 05 had a similiar problem the battery light flicked a few times then stayed on then went off, this was at normal driving speed.. I had the battery/alt checked at auto store and it was putting out proper voltage and showed it was charging. So, after couple weeks seemed ok then it did it again and during this time everything seemed to be working ok, belts an all looked good. Was a little timid about driving more and possibly getting stranded. I don't drive it as much as most do. A few days later went out and after a few miles it started to flicker then stayed on. So headed back home and things on the dash started lighting up like a christmas tree. Luckly I made it home - in limp mode - would only go fast enough to get there. RESULTS- alt went and 400 bucks later seems all good now, no lights! For those who know: THIS ALT REPLACEMENT CAN BE VERY COSTLY IF YOU CAN'T DO IT YOURSELF OR HAVE SOMEONE WHO CAN, for me a guy who does my work was a blessing, got a replacement alt(150/200 amp) and changed it out. Probably like 1000 bucks at VW service and their alt !!!
 

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My 05 had a similiar problem the battery light flicked a few times then stayed on then went off, this was at normal driving speed.. I had the battery/alt checked at auto store and it was putting out proper voltage and showed it was charging. So, after couple weeks seemed ok then it did it again and during this time everything seemed to be working ok, belts an all looked good. Was a little timid about driving more and possibly getting stranded. I don't drive it as much as most do. A few days later went out and after a few miles it started to flicker then stayed on. So headed back home and things on the dash started lighting up like a christmas tree. Luckly I made it home - in limp mode - would only go fast enough to get there. RESULTS- alt went and 400 bucks later seems all good now, no lights! For those who know: THIS ALT REPLACEMENT CAN BE VERY COSTLY IF YOU CAN'T DO IT YOURSELF OR HAVE SOMEONE WHO CAN, for me a guy who does my work was a blessing, got a replacement alt(150/200 amp) and changed it out. Probably like 1000 bucks at VW service and their alt !!!
A different fault entirely, your symptoms were typical of an alternator with worn brushes.
 
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